1. Field of the Invention
This invention relates generally to internal combustion engines, and pertains more particularly to apparatus for determining the time the valves open and close, as well as the amount of lift and the duration of valve opening.
2. Description of the Prior Art
A relatively large number of mechanisms have been devised for controlling the opening and closing of inlet and exhaust valves for internal combustion engines. In this regard, some are quite simple, but perform only one function, such as controlling the height of valve opening, frequently referred to as the valve lift. Others have controlled the period or duration of valve opening without varying the lift.
One relatively early patent which depicts a mechanism for adjusting only the valve lift is U.S. Pat. No. 1,395,851, issued Nov. 1, 1921, to Francis B. McLean for "Valve Operating Mechanism". The effective moment arm or leverage for affecting the opening of the valve is derived from a rocker arm that is pivotally mounted intermediate its ends, the fulcrum or pivot point being shiftable in order to vary the amount of valve lift produced by the valve cam.
A patent depicting a mechanism that determines both the amount of valve lift and the time that the valve remains open is found in U.S. Pat. No. 2,412,457, issued on Dec. 10, 1946 to Laurence D. Harrison for "Valve Actuating Mechanism". The mechanism employs a profiled or contoured adjusting lever or rocker arm that is shifted relative to the valve to be opened and closed. However, the control of the lift and duration are integrated with each other and one cannot be realized in practice without affecting the other. Here again, the predominant change is in the duration, the correlated change in lift being quite minimal.
For the most part, prior art devices for varying the valve lift are indeed quite complicated and relatively costly. Furthermore, some of the devices with which I am acquainted contain parts that are vulnerable to wear with the consequence that their lift span is unduly short. In such instances, the owner would be confronted with the likelihood of frequent and costly repairs, thereby militating against the adoption of such valve actuating mechanisms.